Fundamentals of GeNetics

1. Fundamentals of GeNetics

2. Every living thing – plant or animal, microbe or human being – has a set of characteristics inherited from its parent or parents. Genetics – Study of heredity Inheritance & Genetics

3. Chromosomes & genes • Chromosome - Very long, continuous single piece of DNA, contains many genes • Gene - Sequence of DNA that codes for a protein and thus determines a trait

4. Alleles are the different possibilities for a given trait. • Every trait has at least two alleles (one from the mother and one from the father) • Example: Eye color – Brown, blue, green, hazel What is an Allele? Examples of Alleles: A = Brown Eyes a = Blue Eyes B = Green Eyes b = Hazel Eyes

5. Homologous Chromosomes - Term used to refer to chromosomes that each have a corresponding chromosome from the opposite-sex parent. • Both chromosomes have all the same genes in the same location, but different ‘versions’ of those genes. Homologous chromosomes

6. Haploid - Term used to refer to a cell that contains only a single set of chromosomes and therefore only a single set of genes; “one set”; represented by N. Diploid - Term used to refer to a cell that contains both sets of homologous chromosomes; “two sets”; represented by 2N. Haploid vs. Diploid

7. Gamete - A mature sexual reproductive cell that has a haploid numbers that unites with another cell to form a new organism. • Example: Sperm or egg cell • Zygote - The cell formed by the union of two gametes. Gamete vs. Zygote

8. Diploid zygote Haploid sperm (gamete) Haploid egg (gamete) 1n 1n 2n Sexual Reproduction - Process by which two cells from different parents unite to produce the first cell of a new organism. + =

9. …which grows into a DIPLOID fetus HAPLOID gametes join… …to form a DIPLOID zygote Remember, in SEXUAL reproduction…

10. Sexual Reproduction – Process by which two cells from different parents unite to produce the first cell of a new organism. Sexual reproduction

11. Meiosis - Process by which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell; Haploid (N) gamete cells are produced from diploid (2N) cells. Meiosis Begin with Diploid (2N) Cells Produce Haploid (N) Cells

12. Four gametes are made during cell division by meiosis. The gamete cells have half the number of chromosomes as the original cell.

13. Meiosis usually involves two distinct divisions: • Meiosis 1 • Meiosis 2 Meiosis

14. Prior to meiosis I, each chromosome is replicated. • The cells then begin to divide in a way that looks similar to mitosis. • One big difference: • Each chromosome pairs with its corresponding homologous chromosome to form a structure called a tetrad and exchange portions of their chromatids in a process called crossing-over. Meiosis 1

15. Tetrad - Structure containing 4 chromatids that forms during meiosis Crossing Over- Process in which homologous chromosomes exchange portions of their chromatidsor alleles. Meiosis 1

16. Produces new combinations of alleles. • Meiosis 1 is similar to mitosis except: • The two cells produced by meiosis I have sets of chromosomes and alleles that are different from each other and from the diploid cell that entered meiosis I. Crossing Over

17. Two cells produced by meiosis I now enter a second meiotic division. Unlike the first division, neither cell goes through a round of chromosome replication before entering meiosis II. Those four daughter cells now contain the haploid number (N)—just 2 chromosomes each. Meiosis 2

18. In male animals, the haploid gametes produced by meiosis are called sperm. • In female animals, generally only one of the cells produced by meiosis is involved in reproduction. This female gamete is called an egg in animals. • In females, cell divisions at the end of meiosis I and meiosis II are uneven. • A single cell, which becomes an egg, receives most of the cytoplasm. • The other three cells are known as polar bodies and usually do not participate in reproduction. Gamete Formation

20. The most common error in meiosis occurs when homologous chromosomes fail to separate. • This is known as nondisjunction. • Results in abnormal numbers of chromosomes in gametes. • Example - Down syndrome, which results when an individual has three copies of chromosome 21. NONdisjunction

21. Mitosis: Produces two genetically identical diploid cells. Meiosis: Produces four genetically different haploid cells. Mitosis vs. Meiosis

22. Mitosis • Allows an organism's body to grow and replace cells. • Used in asexual reproduction to produce a new organism. • New (daughter) cell is identical to the parent celland to each other. • Produces two diploid (2N) daughter cells. • Meiosis • Used in sexual reproduction to produce gametes. • New (daughter) cells are genetically different from the parent cells and from one another. • Produces four haploid (N) cells. • Is responsible for the genetic variation among species. Mitosis vs. Meiosis

23. You can only inherit a trait from gametes, not other somatic (body) cells! Mutations within somatic (body) cells do not affect future offspring genes. Whereas, mutations within gametes do alter offspring genes. For example, if your mother has skin cancer, you will not inherit this mutation because the mutation is on her somatic (body) cells and these are not inherited. Inheritance & Cell type

24. Mendel carried out his work with ordinary garden peas. • Mendel studied 7 different pea plant traits such as seed color or plant height. • Trait - Specific characteristic that varies from one individual to another. • Each of the 7 traits Mendel studied had two contrasting characters. • For example, green seed color and yellow seed color. Gregor Mendel

25. Mendel crossed plants with each of the seven contrasting characters and studied their offspring. • Parental or P Generation - Each original pair of plants • F1 or First Generation– The first set of offspring from the parents Gregor Mendel’s Experiments

26. Mendel crossed a tall and short plant and all offspring were tall. • All of the offspring had the character of only one of the parents. • Mendel concluded that some alleles are dominant and others are recessive (called the Principle of Dominance) Gregor Mendel’s first set of Experiments

27. He then crossed the F1 generation with itself to produce the F2offspring (Tall x Tall) • Some of the traits had reappeared - some were tall and some were short. • The Law of Segregation was concluded (the two alleles segregate from each other so that each gamete carries only a single copy of each gene). Gregor Mendel’s second set of Experiments

28. Crossed round, yellow pea plants with wrinkled, green pea plants • All offspring were round yellow peas • He then crossed those offspring (F1) together to produce the F2 generation and the offspring were a mixture of all traits. Mendel's LATER Experiments: Two-Factor CrossEs

29. Mendel concluded that genes for different traits can segregate independently during the formation of gametes (called the Law of Independent Assortment) • These genes that segregate independently do not influence each other’s inheritance. • Helps account for the many genetic variations observed in plants, animals, and other organisms. Mendel's conclusions from his Two-Factor CrossEs

30. Dominant - Masks the other trait; the trait that shows if present • Represented by a capital letter • Recessive – An organism with a recessive allele for a particular trait will only exhibit that trait when the dominant allele is not present; Will only show if both alleles are present • Represented by a lower case letter Dominant vs. Recessive R r

31. TT - Represent offspring with straight hair • Tt - Represent offspring with straighthair • tt - Represents offspring with curly hair Dominant & Recessive Practice T – straight hair t - curly hair

32. Homozygous – Term used to refer to an organism that has two identical alleles for a particular trait (TT or tt) • Sometimes called purebred • Heterozygous - Term used to refer to an organism that has two different alleles for the same trait (Tt) • Sometimes called hybrid Homozygous vs. Heterozygous RR rr Rr

33. Genotype – The genetic makeup of an organism; The gene (or allele) combination an organism has. • Example: Tt, ss, GG, Ww • Phenotype – The physical characteristics of an organism; The way an organism looks • Example: Curly hair, straight hair, blue eyes, tall, green Genotype vs. Phenotype

34. Punnett Square – Diagram showing the gene combinations that might result from a genetic cross • Used to calculate the probability of inheriting a particular trait • Probability – The chance that a given event will occur Punnett Squares

35. Punnett Square Parent Parent Offspring

36. How to Complete a Punnett Square

37. Y-Yellow y-white Genotype: 1:2:1 (YY:Yy:yy) 25%, 50%, 25% Phenotype: 3 Yellow, 75% 1 White, 25%

38. Give the genotype and phenotype for the following cross: TT x tt (T = Tall and t = Short) You Try It Now!

39. Step One: Set Up Punnett Square (put one parent on the top and the other along the side) T T t t TT x tt

40. Step Two: Complete the Punnett Square T T t t TT x tt

41. Step Three: Write the genotype and phenotype T T t t TT x tt Genotype: 4 – Tt or 100% Phenotype: 100% Tall Remember: Each box is 25%

42. Give the genotype and phenotype for the following cross: Tt x tt You Try It Now!

43. Step One: Set Up Punnett Square (put one parent on the top and the other along the side) T t t t Tt x tt

44. Step Two: Complete the Punnett Square T t t t Tt x tt

45. Step Two: Complete the Punnett Square T t t t Tt x tt Genotype: Tt - 2 (50%) tt - 2 (50%) Phenotype: 50% Tall 50% Short Remember: Each box is 25%

46. Incomplete Dominance- Situation in which one allele is not completely dominant over another. • Example – Red and white flowers are crossed and pink flowers are produced. Incomplete Dominance

47. Codominance - Situation in which both alleles of a gene contribute to the phenotype of the organism. • Example – A solid white bull is crossed with a solid brown cow and the resulting offspring are spotted brown and white (called roan). • + Codominance

48. Multiple Alleles- Three or more alleles of the same gene. • Even though three or more alleles exist for a particular trait, an individual can only have two alleles - one from the mother and one from the father. Multiple Alleles

49. Coat color in rabbits is determined by a single gene that has at least four different alleles. Different combinations of alleles result in the five colors you see here. Examples of Multiple Alleles

50. Blood Type – 3 alleles exist (IA, IB, and i), which results in four different possible blood types • Hair Color – Too many alleles exist to count • There are over 20 different shades of hair color. Examples of Multiple Alleles